1. Field of the Invention
This invention pertains to a field coil for actuating an electromagnetically clutch, particularly an automotive accessory drive clutch.
2. Description of the Prior Art
Field coil assemblies in the prior art conventionally include a coil of copper wire in the form of a torus, the coil being located in a housing partially enclosing the coil. Usually the housing contains a space having the general shape of the wire coil, the space being larger than that of the coil to allow locating the coil within the housing. Then, the ends of the wire are lead from the housing to an external terminal connection engageable by an electrical receptacle. The open end of the housing and the space within the housing between the coil and the interior walls of the housing are filled or potted with nonpolymerized plastic resin, which is later cured or polymerized at elevated temperature or room temperature depending upon the duration of a period available to polymerize the resin. The resin flows into the cavity of the housing as a viscous liquid and the ends of the housing are sealed to prevent resin flow from the housing in the less viscous form it has after its temperature is raised and before it polymerizes.
Usually the components of the assembly must be preheated before the epoxy potting is added to the housing, then the resin is heated to the cure temperature and is maintained at that temperature for a predetermined period during which period the resin polymerizes. Care must be taken to assure that the Part has been cooled adequately to room temperature for subsequent handling on an assembly line required to complete the assembly.
Lengthy periods are required to mix the components of the plastic resin, to maintain the mixture at low temperature to prevent its polymerizing before being potted in the housing cavity, and to prevent contamination with foreign substances. Furthermore, the process of potting the coil in the housing with the plastic resin is slow, tedious and susceptible to wasted potted material and spotting and dripping on the surfaces of the housing. The costs associated with preheating the components before potting, heating them in an oven to a cure temperature, controlling the cooling rate and guarding against later handling while hot are difficulties with this method of field coil assembly for which solutions have long been sought.